Gate stacks

ABSTRACT

Some embodiments disclose a gate stack having a gate (e.g., polysilicon (poly) material) horizontally between shallow trench isolations (STIs), a tungsten silicide (WSix) material over the gate and the STIs, and a tungsten silicon nitride (WSiN) material on a top surface of the WSix material. Some embodiments disclose a gate stack having a gate between STIs, a first WSix material over the gate and the STIs, a WSiN interlayer material on a top surface of the first WSix material, and a second WSix material on a top surface of the WSiN interlayer material. Additional embodiments are disclosed.

PRIORITY APPLICATION

This application is a continuation of U.S. application Ser. No. 14/688,337, filed Apr. 16, 2015, which is incorporated herein by reference in its entirety.

BACKGROUND

Gate stacks including a tungsten silicide (WSix) material tier with topography may suffer from WSix cracking, which may affect gate functional reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

FIG. 1A is a cross-sectional view illustrating an example of a gate stack according to a first embodiment.

FIG. 1B is a cross-sectional view illustrating a cracked gate stack according to the first embodiment.

FIG. 2 is a cross-sectional view illustrating an example of a gate stack according to a second embodiment.

FIG. 3 is a cross-sectional view illustrating an example of a gate stack according to a third embodiment.

FIG. 4 is a process flow diagram illustrating a process of fabricating a gate stack according to an embodiment.

FIG. 5 is a process flow diagram illustrating a process of fabricating a gate stack according to another embodiment.

DESCRIPTION OF THE EMBODIMENTS

The following detailed description refers to the accompanying drawings which show, by way of illustration, specific aspects and embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter.

The term “horizontal” as used in this application is defined as a plane parallel to the conventional plane or surface of a wafer, such as a substrate, regardless of the actual orientation of the wafer or substrate. The term “vertical” refers to a direction perpendicular to the horizontal as defined above. Prepositions, such as “on”, “side”, “higher”, “lower”, “over” and “under” are defined with respect to the conventional plane or surface being on the top surface of the wafer or substrate, regardless of the actual orientation of the wafer or substrate.

The terms “wafer” and “substrate” are used herein to refer generally to any structure on which integrated circuits are formed, and also to such structures during various stages of integrated circuit fabrication. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

FIG. 1A is a cross-sectional view illustrating an example of a gate stack 100 according to a first embodiment. The gate stack 100 may include an NAND complementary metal-oxide semiconductor (CMOS) gate. In some embodiments, the gate stack 100 may include a gate 10 formed horizontally between shallow trench isolations (STIs) 20 (e.g., silicon oxide), and a WSix material 30 formed over the gate 10 and the STIs 20. In many situations, the height of the gate 10 is generally different from the height of the STIs 20. As shown in FIG. 1A, for example, the gate 10 is higher than the STIs 20, and thus a top surface of the gate 10 and top surfaces of the STIs 20 are not on a same level. In some embodiments, the gate 10 may include a polysilicon (poly) material. Weak spots 30A may be formed at low material density regions as deposited due to topography, and may cause integration issues within the gate stack 100. In some embodiments, the gate stack 100 may further include a gate oxide 40 (e.g., silicon oxide), which is formed vertically between the gate 10 and a channel 50. The channel 50 may include a single crystalline silicon active area.

FIG. 1B is a cross-sectional view illustrating a cracked gate stack 100 according to the first embodiment. Over some processing steps during a fabrication of the gate stack 100 with topography, WSix grains may grow, and may thus introduce volume shrinkage and large tensile stress, which may cause some open cracks 30B at low density areas (such as weak spots 30A as shown in FIG. 1A). For example, during the fabrication of the gate stack 100, after receiving a thermal treatment with a thermal budget, cracks 30B may be formed at the weak spots 30A of the WSix material 30. Such cracks 30B may result in broken gate reliability, and thus may yield concerns to the gate stack 100.

FIG. 2 is a cross-sectional view illustrating an example of a gate stack 200 according to a second embodiment. In some embodiments, the gate stack 200 may include a gate 10 formed between STIs 20, a WSix material 30 formed on a top surface of the poly material 10 and top surfaces of the STIs 20, and a tungsten silicon nitride (WSiN) material 60 as a cap on a top surface of the WSix material 30. In some embodiments, the WSiN material 60 has a thickness in a range from 50 A to 200 A. Weak spots 30A (as shown in FIG. 1A) may be formed at low material density regions due to topography.

Compared with the WSix material 30, the WSiN material 60 may have a higher resistance to grain growth under a thermal treatment, may experience smaller volume shrinkage and stress build-up, and thus may be more stable than the WSix material 30 during the thermal treatment. The WSiN material 60 in the gate stack 200 may function as both a stress stabilization layer and a crack propagation barrier to limit the crack formation and propagation. Such a hybrid WSix/WSiN stack structure may mitigate possible WSix cracking of the WSix material deposited on the gate stack with topography. A crack-free gate stack may thus be achieved with such a hybrid WSix/WSiN stack.

In some embodiments, the gate stack 200 may further include a dielectric material (e.g., tetraethyl orthosilicate (TEOS)) 70 formed on a top surface of the WSiN material 60. In some embodiments, the gate stack 200 may further include a gate oxide 40 fainted between the poly material 10 and a channel 50. The channel 50 may include a single crystalline silicon active area. The gate stack 200 may include a source and a drain (not shown in the figures). The gate stack 200 may be used in a peripheral transistor of a three dimension (3D) NAND flash memory or other memories such as a planar nonvolatile memory or a volatile memory.

FIG. 3 is a cross-sectional view illustrating an example of a gate stack 300 according to a third embodiment.

In some embodiments, the gate stack 300 may include a gate 10 formed between STIs 20, a first WSix material 30 formed on a top surface of the gate 10 and top surfaces of the STIs 20, a WSiN interlayer material 60 on a top surface of the first WSix material 30, and a second WSix material 80 on a top surface of the WSiN interlayer material 60. In some embodiments, a thickness of the WSiN interlayer material 60 is approximately of 50 A to 200 A. Weak spots 30A may be formed at low material density regions as deposited due to topography.

Compared with a WSix material (such as the first WSix material 30 and the second WSix material 80), the WSiN interlayer material 60 may have a higher resistance to grain growth under a thermal treatment, may experience smaller volume shrinkage and stress build-up, and thus may be more stable than the WSix material during the thermal treatment. The WSiN interlayer material 60 in the gate stack 300 may function as both a stress stabilization layer and a crack propagation barrier to limit the crack formation and propagation. For example, even when cracks are formed in the first WSix material 30, the WSiN interlayer 60 may block the cracks to prevent the cracks from propagating through the whole stack. Therefore, such a hybrid WSix/WSiN/WSix stack structure may mitigate possible WSix cracking of the WSix material deposited on the gate stack with topography. A crack-free gate stack may thus be achieved with such a hybrid WSix/WSiN/WSix stack. The gate stack 300 may be used in a peripheral transistor of a 3D NAND flash memory or other memories such as a planar nonvolatile memory or a volatile memory.

In some embodiments, the gate stack 300 may further include a TEOS material formed over the second WSix material 80. In some embodiments, the gate stack 300 may further include a gate oxide 40 formed between the poly material 10 and a channel 50. The gate stack 300 may include a source and a drain (not shown in the figures).

FIG. 4 is a process flow diagram illustrating a process 400 of fabricating a gate stack 200 as shown in FIG. 2 according to an embodiment.

At 402, a gate structure may be formed on a substrate (such as a silicon material). The gate structure may include a gate 10 (such as a poly material) horizontally between STIs 20 (e.g., silicon oxide) as shown in FIG. 2. In some embodiments, the gate structure may further include a gate oxide 40 formed vertically between the poly material 10 and a channel 50. The channel 50 may include a single crystalline silicon active area. The gate structure may include a source and a drain (not shown in the figures).

At 404, a WSix tier 30 may be formed over the gate 10 and the STIs 20. In some embodiments, in a Physical Vapor Deposition (PVD) chamber, WSix may be deposited on the top surface of the gate 10 and the top surfaces of the STIs 20 to form the WSix tier 30.

At 406, a WSiN tier 60 may be formed on a top surface of the WSix tier 30 as a cap. In some embodiments, in the chamber (e.g., the PVD chamber used to form the WSix tier 30), a WSix material may be sputtered on the top surface of the WSix tier 30, while adding nitrogen gas into the chamber, to incorporate nitrogen into the sputtered WSix material to form the WSiN tier 60. In some embodiments, in the chamber used to form the WSix tier 30, a WSiN material may be directly sputtered on the top surface of the WSix tier 30 to form the WSiN tier 60.

These methods of fabricating a gate stack are flexible, and the whole fabrication process can be done in the same PVD chamber for example. In this way, it can be easier to control the location and thickness of the WSix tier 30 and the WSiN tier 60 individually in the hybrid WSix/WSiN stack. Additionally, these methods of fabricating a gate stack are integration-friendly. The WSix tier 30 in the hybrid WSix/WSiN stack may act as an interface layer, and the WSiN tier 60 (with nitrogen up to e.g., 13%) may not provide any dry etch concerns due to the small amount of nitrogen.

In some embodiments, in an implant chamber, nitrogen may be implanted into an upper portion of the WSix tier 30 to transform the upper portion of the WSix material into a WSiN material to form the WSiN tier 60.

In some embodiments, a dielectric material (e.g., TEOS) tier 70 may be formed on a top surface of the WSiN tier 60.

FIG. 5 is a process flow diagram illustrating a process 500 of fabricating a gate stack 300 according to another embodiment.

At 502, a gate structure may be formed on another material, such as a substrate. The gate structure may include a gate 10 (such as a poly material) horizontally between STIs 20 (e.g., silicon oxide) as shown in FIG. 3. In some embodiments, the gate structure may further include a gate oxide 40 formed vertically between the gate 10 and a channel 50. The channel 50 may include a single crystalline silicon active area.

At 504, a first WSix tier 30 may be formed over the gate 10 and the STIs 20. In some embodiments, in a chamber (e.g., a PVD chamber), WSix may be deposited on the top surface of the gate 10 and the top surfaces of the STIs 20 to form the first WSix tier 30.

At 506, a WSiN interlayer tier 60 may be formed on a top surface of the first WSix tier 30.

In some embodiments, in the PVD chamber used to form the first WSix tier 30, while adding nitrogen gas into the chamber, a WSix material may be sputtered on the top surface of the first WSix tier 30 to incorporate nitrogen into the sputtered WSix to form the WSiN interlayer tier 60. In some embodiments, in the PVD chamber used to form the first WSix tier 30, a WSiN material may be directly sputtered on the top surface of the first WSix tier 30 to form the WSiN interlayer tier 60. In some embodiments, in an implant chamber, nitrogen may be implanted into an upper portion of the first WSix tier 30 to transform the upper portion of the WSix material into a WSiN material to form the WSIN interlayer tier 60.

At 508, a second WSix tier 80 may be formed on a top surface of the WSiN interlayer tier 60. In some embodiments, in the same PVD chamber used to form the first WSix tier 30 and the WSiN interlayer tier 60, a WSix material may be directly deposited to form the second WSix tier 80 on the top surface of the WSiN interlayer tier 60.

In some embodiments, a dielectric material (e.g., TEOS) tier 70 may be formed over the second WSix tier 80.

The above description and the drawings illustrate some embodiments of the invention to enable those skilled in the art to practice the embodiments of the invention. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Examples merely typify possible variations. Portions and features of some embodiments may be included in, or substituted for, those of others. Many other embodiments will be apparent to those of ordinary skill in the art upon reading and understanding the above description. 

The invention claimed is:
 1. A memory device comprising: a memory array; and a peripheral transistor coupled to the memory array, the peripheral transistor comprising: a gate between shallow trench isolations (STIs) and directly contacting the STIs, a height of the gate being different from a height of the STIs; a tungsten silicide (WSix) material on a top surface of the gate and top surfaces of the STIs; and a tungsten silicon nitride (WSiN) material on a top surface of the WSix material.
 2. The memory device of claim 1, wherein the memory device comprises a three dimensional (3D) NAND flash memory device, a planar non-volatile memory device, or a volatile memory device.
 3. The memory device of claim 1, wherein the peripheral transistor further comprises a dielectric material over the WSiN material, and wherein the dielectric material comprises tetraethyl orthosilicate (TEOS).
 4. The memory device of claim 1, wherein the peripheral transistor further comprises a channel under the gate, and wherein the channel comprises silicon.
 5. The memory device of claim 4, wherein the peripheral transistor further comprises a gate oxide between the gate and the channel.
 6. The memory device of claim 1, wherein the STIs comprise silicon oxide, and wherein the gate comprises a polysilicon (poly) material.
 7. A memory device comprising: a memory array; and a peripheral transistor coupled to the memory array, the peripheral transistor comprising: a gate between shallow trench isolations (STIs) and directly contacting the STIs, a height of the gate being different from a height of the STIs; a first tungsten silicide (WSix) material on a top surface of the gate and top surfaces of the STIs; a tungsten silicon nitride (WSiN) interlayer material on a top surface of the first WSix material; and a second WSix material on a top surface of the WSiN interlayer material.
 8. The memory device of claim 7, wherein the memory device comprises a three dimensional (3D) NAND flash memory device, a planar nonvolatile memory device, or a volatile memory device.
 9. The memory device of claim 7, wherein the peripheral transistor further comprises a tetraethyl orthosilicate (TEOS) material over the second WSix material.
 10. The memory device of claim 7, wherein the peripheral transistor further comprises: a channel under the gate; and a gate oxide between the gate and the channel.
 11. A three dimensional (3D) NAND memory device comprising: a NAND memory array; and a peripheral transistor coupled to the NAND memory array, the peripheral transistor comprising: a gate between first and second dielectric materials and directly contacting the first and second dielectric materials, the gate including a height different from a height of each of the first and second dielectric materials; a silicide material on a top surface of the gate and on top surfaces of the first and second dielectric materials; and a combination of metal and silicon nitride material on a top surface of the silicide material.
 12. The 3D NAND memory device of claim 11, further comprising a second silicide material on a top surface of the combination of the metal and silicon nitride material.
 13. The 3D NAND memory device of claim 11, wherein the silicide material comprises tungsten silicide (WSix).
 14. The 3D NAND memory device of claim 13, wherein the combination of metal and silicon nitride comprises tungsten silicon nitride (WSiN).
 15. The 3D NAND memory device of claim 14, wherein the second silicide material comprises tungsten silicide (WSix).
 16. The 3D NAND memory device of claim 14, further comprising an oxide extending over the WSiN material.
 17. The 3D NAND memory device of claim 11, wherein the first and second dielectric materials comprise silicon oxide.
 18. The 3D NAND memory device of claim 11, wherein the peripheral transistor further comprises a gate oxide under the gate and between the first and second dielectric materials and directly contacting the first and second dielectric materials.
 19. The 3D NAND memory device of claim 11, wherein the peripheral transistor further comprises a channel under the gate oxide and between the first and second dielectric materials, the channel directly contacting the first and second dielectric materials. 